Horizontally acquired cysteine synthase genes undergo functional divergence in lepidopteran herbivores

Horizontal gene transfer (HGT) plays an important role in evolutionary
processes as organisms adapt to their environments, and now cases
of gene duplication after HGT in eukaryotes are emerging at an
increasing rate. However, the fate and roles of the duplicated
genes over time in eukaryotes remain unclear. Here we conducted a
comprehensive analysis of the evolution of cysteine synthase
(CYS) in lepidopteran insects. Our results indicate
that HGT-derived CYS genes are widespread and have undergone
duplication following horizontal transfer in many lepidopteran
insects. Moreover, lepidopteran CYS proteins not only have β-cyanoalanine
synthase activity but also possess cysteine synthase activity that is
involved in sulfur amino acid biosynthesis. Duplicated CYS genes
show marked divergence in gene expression patterns and enzymatic
properties, suggesting that they probably have
undergone subfunctionalization and/or neofunctionalization in
Lepidoptera. The gene transfer of CYS genes and subsequent
duplication appears to have facilitated the adaptation of lepidopteran
insects to different diets and promoted their ecological
diversification. Overall, this study provides valuable insights
into the ecological and evolutionary contributions of CYS in lepidopteran
insects.